1. Field of the Invention
The present invention relates to a fuel storage canister for use in an engine fuel supply system, and more particularly to a fuel storage canister for preventing fuel from being evaporated into the atmosphere while an engine is not operating.
2. Description of the Relevant Art
U.S. Pat. No. 4,951,643 discloses a closed-bottom fuel storage canister having a fuel storage section in a lower portion of a canister housing and an activated carbon layer above the fuel storage section. The fuel storage section of the disclosed fuel fuel storage canister communicates with the fuel tank of an automobile through a charge pipe, and also with the intake manifold of the engine of the automobile through a purge pipe. The fuel storage section is vented to the atmosphere through the activated carbon layer and a drain outlet defined in an upper portion of the housing.
In the conventional fuel storage canister, while the engine is not operating, a high-boiling-point component of the fuel vapor tends to be adsorbed by the activated carbon layer, which is then saturated. If the engine remains out of operation for a long period of time without the high-boiling-point component being purged, then a low-boiling-point component of the fuel vapor inevitably passes through the activated carbon layer into the atmosphere.
Japanese laid-open patent publication No. 1-159455 published Nov. 18, 1987 shows a canister having a first space section, a first fuel vapor adsorbent, a section space section, a second fuel vapor adsorbent, and a third space section which are successively positioned and defined in a casing. The first space section is connected from an inlet port to the fuel tank of an automobile through a valve that is opened only when fuel is supplied to the fuel tank. The first space section also communicates with the intake manifold of the engine of the automobile from a purge port. The third space section is vented to the atmosphere from an atmosphere port.
According to the above prior canister, the first and second adsorbents are positioned between the first space section connected to the fuel tank and the third space section vented to the atmosphere. Therefore, while the engine is not operating, a high-boiling-point component of the fuel vapor is adsorbed by the first and second adsorbents, which are then saturated. A low-boiling-point component of the fuel vapor is also inevitably caused to pass into the atmosphere while the engine is not operating. Particularly, the first and second adsorbents are liable to suffer aging as they are exposed to the fuel vapor at all times.